1. Field of the Invention
The invention relates to a method and apparatus for melting metals, particularly light, heavy and noble metals, as well as the alloys thereof, in crucibles or trays by combustion of liquid, gaseous or solid fuels, and by exhaust gases produced by such fuels.
2. Discussion of the Prior Art
In order to improve thermal efficiency in the melting of metals, a number of proposals have been made, one of which is to use a crucible melting furnace with a pre-melter through which the furnace exhaust gases flow, as disclosed in German patent 444 535. One disadvantage of such furnaces is that the dirt particles carried along by the furnace exhaust gases are deposited on the metal to be pre-heated, which leads to considerable contamination and gas penetration of the melting bath when new material is introduced to re-charge the bath.
An attempt to eliminate these short-comings by an indirectly heated pre-heating chamber is described in German patent publication AS No. 12 10 132. The proposal there was to separate the pre-heating chamber, in which the scrap was heated, from the exhaust gas flues by a gas-tight partition. Although this eliminated the above-mentioned disadvantages regarding the feeding of dirt particles onto the metal to be pre-heated, the thermal efficiency could not be increased nor fully utilized because of the relatively low thermal conductivity of the partition, especially since the material to be melted is heated from only one side (from below), and heat transfer through radiation (from above) is not sufficient.